The invention is related to the field of waveguides, and in particular to a quasi-two-dimensional gyrotropic photonic crystal used as a one-way microwave waveguide.
Photonic crystals are structures that are specifically engineered to have periodicity comparable to the wavelength of light. Such devices, which were invented in the late 1980s, possess many interesting optical properties. Their underlying theoretical description relies on an analogy between (i) the equations of classical electromagnetism in a periodic medium, and (ii) the equations of quantum mechanics in a periodic potential. The latter is most commonly used to describe the physics of electrons in a crystalline solid, which has long been a basic part of “condensed-matter” (or “solid-state”) physics. Many phenomena that occur in condensed-matter systems have been observed in photonic crystal systems.
The unique physical phenomena that occur in both photonic crystals and electrons in crystalline solids are referred as “band effects”. The electromagnetic modes in a photonic crystal fall into “bands”—discrete ranges of energy and frequency—similar to the electronic bands that occur in a solid. Between the bands lie “band gaps”, ranges of energy and frequency in which no propagating modes exist. Note, however, that despite the strong theoretical analogies between photonic crystal modes and electron states, their underlying physical natures are quite different: the former are propagating disturbances in the electromagnetic field, while the latter are quantum mechanical states of matter.
The length-scale of a photonic crystal determines the range of frequencies at which band effects occur. To observe band effects at the frequency of visible light, a photonic crystal must have a crystalline lattice spacing of around 0.5 micrometers. In the present patent, for reasons that will be described below, we will mostly be concerned with band effects that occur at microwave frequencies. These are produced in photonic crystals with lattice spacings of about a centimeter.